174 The Rothamsted Agricultural Experiments. 
plot there are only ten species of plants altogether, and 99-8% of the 
dry weight of the crop is composed of grasses, almost entirely of three 
species. This crop usually goes flat before cutting, and is particu- 
arly liable to the attacks of fungi. 
Treatment with a mixed mineral manure, including the indi¬ 
spensable potash, but excluding nitrogen, has caused a great 
increase of leguminous plants (mainly clover), which sometimes 
form 50% of the dry weight of the crop. This is of course because 
these plants, being independent of combined. nitrogen, when they 
are supplied with the indispensable potassium, gain a great advan¬ 
tage over the grasses, which do require combined nitrogen. There 
are, however, actually more grasses in the hay of this plot than in 
that of an unmanured plot, because these plants live at the expense of 
the combined nitrogen in the humus formed by the leguminous 
plants. 
The specialisation of the vegetation, according to whether the 
food-constituents in the manures are retained at the surface or 
penetrate more deeply into the soil, is also very clearly brought out. 
Thus the plots manured with ammonium salts bear a shallow- 
rooted vegetation with such grasses as Festuca ovina and Anthoxan- 
tlmm odoratum, while those manured with sodium nitrate give 
deep-rooted crops with Brovins mollis and Avena elatior dominant. 
The plot manured with a complete manure, the nitrogen as sodium 
nitrate, is also strikingly characterised by the abundance of Authriscus 
sylvestris, which, as is well-known, ordinarily frequents hedge sides 
and the shade of trees, often in company with Brovins. Why the 
nitrate manuring should encourage it in the open is not at all obvious. 
We have only alluded to a few of the more important con¬ 
clusions that may be deduced from this extremely beautiful series of 
experiments. They suggest subjects for fresh enquiry on every 
hand. Perhaps the most important general lesson is the emphasis 
given to the keen competition of different species in the struggle 
for existence, and the enormous advantage given to certain species 
over others by comparatively slight alterations in the conditions of 
life. The working of some of these alterations we are able to trace, 
while others still remain a mystery ; but there can be no doubt that 
long continued systematic experiment of this kind is the surest 
means of throwing light on the often perplexing combinations of 
species in natural floras. 
Wheat. 
Broadbalk Field, about eleven acres in extent, has been con- 
